The present invention relates to an internal combustion engine with a plurality of cylinders, comprising an inlet conduit which conducts inlet air to the cylinders of the engine, two separate exhaust manifolds each receiving exhaust from an individual group of cylinders, a charging unit, the pressure side of which communicates with the inlet air conduit, a conduit leading from each exhaust manifold to the inlet air conduit for recirculation of exhaust from the exhaust side of the engine to its inlet side, and valve means communicating with respective recirculation conduit and having control means disposed, under those conditions when exhaust is to be recirculated, to open the valve means when the exhaust pressure in the respective exhaust manifold is higher than the inlet pressure on the pressure side of the charge unit.
In supercharged internal combustion engines, e.g. turbo engines, the charge pressure of the inlet air in the inlet manifold is often higher than the average pressure of the exhaust in the exhaust manifold, which means that conventional damper and valve means used in suction engines, cannot immediately be used in supercharged engines to return the exhaust to the pressure side of the compressor. In order to achieve this it is known to use some pressure increasing means on the exhaust side, e.g. a constriction in the form of a turbo unit with variable geometry, or some kind of pump device.
If the pressure increase principle is used, it means that the engine will operate against a pressure with its entire exhaust flow to return only a fraction of the flow, e.g. only about 10%, to the inlet side, which results in an undesirable loss of efficiency. The pump principle, in addition to involving extra expense and complication, involves a parasite loss corresponding to the pressure increase of about 10% of the exhaust flow divided by the efficiency of the pump, i.e. a total of about 20% of the exhaust flow times the pressure increase.
By SE-A-9603028-3 it is known in an internal combustion engine with exhaust recirculation in the recirculation conduit to arrange valve means with valve control means, which control the valve means so that during those operating conditions when exhaust is to be recirculated, the valve means only open when the exhaust pressure in the manifold is higher than the inlet pressure on the pressure side of the charge unit. This solution, which is much simpler and less expensive than a pump device and permits exhaust to be returned to the inlet side without any loss of efficiency, is based on the fact that the pressure during pressure pulsations in the exhaust manifold has pressure tops exceeding the charge pressure in the inlet manifold, and uses valve means which open during the pressure tops but which are kept closed therebetween to prevent inlet air from flowing to the exhaust side.
The purpose of the present invention is to achieve an internal combustion engine with valves in the exhaust recirculation conduit controlled in this manner, which permits higher mass flow of recirculated gas to the pressure side of the charger than what has hitherto been possible.
This is achieved according to the invention by virtue of the fact that the inlet air conduit comprises an equalisation chamber, two separate inlet manifolds and two resonance pipes, each of which joins the equalisation chamber with an individual inlet manifold to an individual group of cylinders, said inlet manifolds each communicating via an individual recirculation conduit with an individual exhaust manifold, and that control means are disposed to open the valve means when the exhaust pressure is higher than the pressure in the inlet manifolds.
By using the principle, known per se with an equalizing chamber and tuned resonance pipes from separate inlet pipes together with the control, also known per se, of the exhaust recirculation valves, it has been demonstrated that the mass flow of recirculated exhaust has been able to be increased to a surprising degree, under certain operating conditions as much as 50% over an inlet system without tuned resonance pipes.